1. Filed of the Invention
The present invention relates to a continuous liquid medicine injector for sequentially injecting a liquid medicine, accommodated in a liquid medicine accommodating portion, into a human body. More particularly, the present invention concerns an improvement in a means for controlling the flow rate of a liquid medicine which is injected from a liquid medicine accommodating portion into a human body.
2. Description of the Related Art
Methods of continuously injecting a liquid medicine into a human body are known. In one such method, a liquid medicine in an injector is manually or automatically supplied into the body through a needle or a catheter. In another method, a liquid medicine in an instillator is naturally or automatically supplied into the body.
In all of the above-described injecting methods, it takes from a few minutes to a few hours for all the drugs to be injected. During that time, a needle or the like has to be connected to a syringe or the like, and this may cause pain to the patient or limit what he or she is able to do during the injection. It may also be necessary for the operator, who may be a doctor or a nurse, to hold a syringe or check the amount of liquid medicine given by an intravenous drip injection, making the injection procedure a troublesome task.
Accordingly, a small and easy-to-handle continuous liquid medicine injector (a catheter) which does not limit the actions of a patient or an operator has been proposed (in, for example, the specifications of Japanese Patent Publication No. 61-51901 and Japanese Patent Laid-Open Nos. 62-11464 and 62-11465).
All of these conventional continuous liquid medicine injectors incorporate a balloon made of an elastic material An inlet portion from which a liquid medicine is sucked into the balloon is provided at one end of the balloon, and an outlet portion from which the liquid medicine is forced out of the balloon is provided at the other end thereof The inlet portion is provided with a check valve which allows the liquid medicine to flow into the balloon but does not permit it to flow out of it. In the conventional continuous liquid medicine injector arranged in the above-described manner, the liquid medicine accommodated in the balloon is forced out of it from the outlet portion due to the contraction of the balloon and is caused to flow into the body through an instrument inserted into a human body such as a needle.
However, all of these continuous liquid medicine injectors involve a problem that the flow of liquid medicine cannot be controlled to a sufficient degree in the outlet portion. This has been an obstacle to practical use of these injectors.
More specifically, in the continuous injector disclosed in the specification of Japanese Patent Publication No. 61-51901, the flow of liquid medicine is controlled by suitably changing the diameter of through-holes formed in the wall of a tube-like body on which the balloon is mounted or by employing a diaphragm which varies the area of the inner diameter of the outlet portion of the tube-like body in accordance with the inner pressure of the balloon. However, control of the diameter of the through-hole formed in the tube wall does not ensure sufficient control of the flow rate due to the thinness of the tube wall. Also, the required diaphragm is difficult to manufacture and its use is therefore, not practical.
Furthermore, in the continuous injector proposed in the specification of Japanese Patent Laid-Open No. 62-11464, control of the flow of liquid medicine is performed by varying the diameter of a thin tube (thin hole) formed in the tube wall in the axial direction of a catheter. However, formation of a thin hole in the axial direction of the thin catheter is difficult, making precise control of the flow rate more difficult.
Furthermore, the continuous injector proposed in the specification of Japanese Patent Laid-Open No. 62-11465 incorporates a liquid medicine flow regulating valve in the outlet portion, and flow control is performed by controlling the restricting ratio of the flow regulating valve. However, precise control is also difficult in this injector, as in the former type of injector.